Refractory crucibles



P 1969 J. c. HOWARD 7 3,440,323

REFRACTORY CRUCIBLE'S Filed July 6, 1966 Sheet of 2' April 2, 1969 J. c.HOWARD 3,440,323

REFRACTORY CRUCIBLES Filed July 6, 1966 Sheet 2 of 2 United StatesPatent 3,440,323 REFRACTORY CRUCIBLES John Christie Howard, Curbar, nearSheflield, England,

assignor to Associated Electrical Industries Limited,

London, England Filed July 6, 1966, Ser. No. 563,256 Int. Cl. H05b 5/14US. CI. 13-30 16 Claims ABSTRACT OF THE DISCLOSURE In a furnace crucibleof the kind having a duct which communicates with two spaced apartregions of the crucible and threads an annular magnetic core, the ductis formed by a plurality of parts each including an outer metal sheathand an inner refractory lining, the parts being releasably connected toeach other and to the crucible so that the duct can be removed andreplaced without dismantling the magnetic core.

This invention relates to refractory vessels such as crucibles andladies and troughs or launders for containing a charge of molten metaland for use in or as, or in conjunction with a furnace capable ofmelting the metal charge and/or maintaining the charge in moltencondition.

Such a refractory vessel generally comprises a main body portion capableof holding the main part of the charge and, except in the case of atrough or launder, a pouring spout or lip which is at an upper end ofthe crucible when the crucible is in a first normal upright positionpermitting no discharge of melt. The melt is discharged through thespout or over the lip when the crucible is tilted into a second pouringposition.

In such a vessel it is essential to maintain the melt at a substantiallyconstant temperature if discharge of the melt is to occur over aprolonged period, for example during controlled pouring of the melt intoa plurality of casting moulds. In order to supply suflicient heat to themelt to maintain it at the desired temperature, the normally lower endof the vessel is provided with an extended portion which includes asubstantially U-shaped duct having its opposite ends communicating withthe inside of the body portion respectively at two spaced apart regions.When the vessel contains a molten metal charge, the metal in the ductand in the body portion forms a closed electrically conducting turn.Induction heating means, including an electric winding inductivelycoupled to the metal in the duct, effect induction heating of the metalin the duct and thereby of the metal in the remainder of the vessel,when suitably energised. The energisation of the winding can be adjustedto maintain the melt at the desired temperature.

With the vessel in use, the rate of erosion of the refractory materialof the crucible is particularly high within the duct where the metalbecomes induction heated. This rate of erosion becomes excessive in thecase of iron, steel and other refractory erosive metals and necessitatesfrequent dismantling and rebuilding of the vessel.

According to the present invention, a refractory vessel for containing acharge of molten metal, comprises a main body portion capable of holdinga substantial part of the charge and a duct having a refractory wall andwhich extends from the normally lower end of the body portion and whichhas its opposite ends communicating with the inside of the body portionrespectively at two spaced apart regions thereof, the duct comprising atleast one part consisting of an outer metal sheath and an innerrefractory lining, the part or parts being releasably 3,440,323 PatentedApr. 22, 1969 connected to the vessel and in the case of a plurality ofparts, to one another so as to permit the part or one or more of theparts to be readily replaced.

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIGURE 1 is a side 'view of a metal pouring furnace including arefractory crucible; and

FIGURE 2 is a sectional view of the furnace shown in FIGURE 1, taken onthe line II-II and looking in the direction indicated by the arrows.

Referring to the drawings, the furnace includes a substantiallycylindrical crucible 2 comprising a suitable refractory lining 4 withinan outer supporting metal casing 6.

The crucible, which is shown in a first normal upright position, has apouring spout 8 provided at its upper end, so that no discharge ofmolten metal is possible from the crucible when it is in this firstposition.

The crucible is supported for tilting by means of a supporting frame 10including two stub axles 12 which lie on a sequential plane of thecrucible and about which the crucible can be tilted to a second pouringposition permitting discharge of metal from the spout 8. The bearingswhich form a support for the stub axles and the means for tilting thecrucible about these axles, are well known in the art and are not shownor described.

A substantially U-shaped duct 14 having a refractory wall extends fromthe base of the crucible and has its two ends communicating with theinside of the crucible respectively at two spaced apart regions. Theduct is formed by three separate parts 16, 18 and 20, each comprising anouter sheath of non-magnetic metal tube 22 having a refractory lining.This lining comprises an outer layer 24 of refractory material which isrammed or cast between the inner surface of the tube 22 and an innerlayer 26 which is a pre-fired tube of refractory material. The adjacentcooperating ends of the parts 16, 18 and 20 are mitered, so that the endfaces of the linings in the tubes can firmly abut one another to ensurethat no leakage of molten metal can occur from the duct at the jointsbetween the parts. The ends of the tubes 22 have outwardly extendingflanges such as 23, to enable the parts to be secured to one another andto the crucible. The flanges may be held together by any suitable meanssuch as quickly detachable clamps (not detailed) which enable the jointsbetween the'flanges to be easily and quickly released, so that any oneor all of the parts may be replaced rapidly when the lining of the ductbecomes excessively eroded.

A closed annular magnetic core 30, which surrounds one limb of the duct14 formed by the part 16, is overwound by a winding 32 connectible to asuitable alternating current source. The winding 32 and the core 39 arearranged so that in use of the crucible, the winding is inductivelycoupled to the closed electrically conducting turn formed by moltenmetal in the duct 14 and molten metal in the body portion of thecrucible. By this means, when the winding is energised to a suitablepower level, the metal in the duct and thereby the metal in the cruciblebecomes induction heated and may be maintained at the desiredtemperature by suitable adjustment of the level of excitation of thewinding. The winding 32 and the core 30 are supported on a framework 34secured to the crucible independently of the duct, so that any or allthe parts of the duct can be replaced without disturbing or interferingwith the induction heating assembly.

In order to prevent the outer metal sheathing of the parts of the duct,with the crucible casing, forming a closed electrically conducting turn,an electrically insulating link is introduced at the joint between atleast one 3 pair of co-operating flanges. This link may be in the formof a shim of a suitable electrically insulating material.

In use of conventional crucibles and in the case of certain metals,notably aluminium, it is believed that the oxides in the melt areincreased as a result of a region of low pressure which exists at thatregion of the melt in the duct having a high coupling factor to theinduction heating winding and which is produced by a constriction of themelt flow area in that region by the induced currents. This effect,known as the pinch effect, normally tends to draw air through the porousrefractory material of the duct. The use of an outer metal sheathingtube for the duct, in the crucible described, produces an airimpermeable layer which inhibits the ingress of air into the melt.

Since the refractory material of the duct merely forms a lining for, andis supported by, the outer metal sheath 22, the quantity of refractorymaterial used in the parts 16, 18 and 20 can be reduced to a minimum.

In the case where the crucible is to be used in conjunction with metaldisplaying a particularly high penetration into the refractory materialused, cooling of the cold face of the lining of the parts 16, 18 or 20may be necessary. Accordingly, as shown in FIGURE 1, a convoluted metaltube 36, which is connectible to a source of cooling fluid, is welded orbrazed to the outer surface of the metal tube 22 and is effective tocool the refractory lining of the parts 16, 18 and 20 in use of thecrucible. Although the parts of the duct have been described as beingconnected together by flanges on the outer metal tubes, it is to beunderstood that any means for securing the parts together, so that theycan easily be dismantled, can be'employed. The parts may for examplehave cooperating stepped ends and may be spigotted together.

To form a good liquid metal seal at the joints between the ends of theparts, a suitable refractory cement may be employed at the joints.

The refractory material of the duct may be selected from a wide varietyof inert refractory ceramics which are available as pre-fired tubes oras monolithic linings, rammed or cast in place. Thus the crucible may beused in conjunction with steel, nickel chromium alloys or otherdifficult charges by a suitable choice of refractory material.

The outer layer of refractory material may be a suitable packedmonolithic refractory material. Thus it can be particulate and fluidicin nature and able to flow sufficiently to seal in use cracks which formin the inner pre-fired refractory layer.

Kit is desired to use a monolithic material for the inner refractorylining, one suitable method of providing it is ram or cast the materialfor the lining about'withdrawable,collapsible or fusible formers. Forexample, if for any particular application the necessary refractory forthe duct lining is not available as a pre-fixed tube, the unfiredmaterial can be rammed into the metal sheath around a tubular metalformer which in use of the crucible will be heated by induction, sofiring the lining in place at the time of filling with the first chargeof metal.

A very important feature of the present invention lies in the rapiditywith which the induction heating duct can be replaced. By the use ofquickly detachable clamps, and by the use of spigotted guides to leadthe duct assembly quickly into the'correct position, very rapid ductrepairs and/or replacement can be effected. It will be appreciated thatthe significant period is that between metal being emptied from thecrucible and its being refilled with molten metal. Metal tight jointsmust be made between the hotscrucible body and the ends of the duct,suitably by a micanite gasket covered on each side with a refractorycement, and it is important that the duct shall be clamped to thecrucible body sufficiently quickly for the clamping pressure to be fullyapplied before the cement cures. The time taken between metal beingemptied and the crucible being refilled after repair or replacement ofthe duct can with a proper working system be brought down to 20 minutesor even 15 minutes.

The relining of the duct itself can also be effected relatively quickly,for example in one or two hours, the existing refractory lining beingdiscarded and the metal sheath being reused.

What I claim is:

1. A refractory vessel suitable for containing a charge of molten metalcomprising:

(a) a main body portion capable of holding a substantial part of thecharge;

(b) a normally lower end to the body portion;

(c) induction heating means including an annular magnetic core; a i

(d) a duct threading the annular core and having first and second ends;

(e) a metal sheath forming an outer part of the duct;

(f) a refractory lining forming an inner part of the duct and disposedinside the metal sheath; and

(g) clamping means by which the duct is releasably secured to thenormally lower ends of the duct in communication with the inside of thebody portion; whereby the duct can be removed and replaced withoutdismantling the induction heating means.

2. A refractory vessel according to claim 1, in which the outer metalsheath is of non-magnetic metal.

3. A refractory vessel according to claim 1, in which the vesselincludes a metal body, the duct is secured to the metal body, and theconnection between the duct and the metal body is such that there is noelectrically continuous path along the duct through the metal sheath andthrough themetal body of the vessel.

4. A refractory vessel according to claim 1, in which the refractorylining comprises an inner pre-fired refractory layer arranged in use tocontact molten metal in the duct, and an outer layer of a suitablepacked monolithic refractory material in contact with the metal sheath.

5. A refractory vessel according to claim 4, in which the inner layer isa pre-fired refractory tube.

6. A refractory vessel according to claim 5, in which the outer layer isparticulate and fluidic in nature and able to flow sufficiently to sealin use cracks which may form in the inner pre-fired refractory layer.

7. A refractory vessel according to claim 1, in which the innerrefractory lining is of monolithic material.

8. A refractory vessel according to claim 1, in which cooling ducts aresecured to the metal sheath in good thermal conductivity therewith.

9. A refractory vessel according to claim 8, in which the cooling ductsare arranged to convey cooling water.

10. A refractory vessel suitable for containing a charge of molten metalcomprising:

(a) a main body portion capable of holding substantially the whole ofthe charge when the vessel is in a normal upright position;

(b) a normally lower end to the body portion;

(c) induction heating means including an annular magnetic core;

(d) a duct threading the annular core and having first and second ends;

(e) a plurality of duct parts assembled together to form different partsof the length of the duct;

(f) a plurality of metal sheaths each forming an outer part of one ofthe duct parts;

(g) a plurality of refractory linings each forming an inner part of oneof the duct parts and disposed within one of the metal sheaths; and

(h) clamping means by which the parts of the duct are releasably securedto the normally lower end of the body portion with thefirst and secondends of the duct in communication with the inside of the body portion;whereby the duct parts can be removed and 5 replaced without dismantlingthe induction heating means.

11. A refractory vessel accordng to claim 10, in which each outer metalsheath is of non-magnetic metal.

12. A refractory vessel according to claim 10, in which the vesselincludes a metal body, the duct is secured to the metal body, and theduct parts are so connected together and to the metal body that there isno electrically continuous path along the duct through the metal sheathsand through the metal body of the vessel.

13. A refractory vessel according to claim 10, in which the refractorylining comprises an inner pre-fired refractory layer arranged in use tocontact molten metal in the duct, and an outer layer of a suitablepacked monolithic refractory material in contact with the metal sheath.

14. A refractory vessel according to claim .13, in which the inner layeris a pre-fired refractory tube.

15. A refractory vessel according to claim 13, in which the outer layeris particulate and fluidic in nature and able to flow sufiiciently toseal in use cracks which may form in the inner pre-fired refractorylayer.

References Cited UNITED STATES PATENTS 2,423,912 7/1947 Tama et al. -313-29 2,939,899 6/1960 Edstrand et al. 13-29 X 3,249,676 5/1966 Rydingeret al 13-30 X 3,334,171 8/1967 Fredrikson et al. 13-29 RICHARD M. WOOD,Primary Examiner.

US. Cl. X.R. 1329

